An oil or gas well typically has a string of tubing through which the well fluid flows. The tubing is suspended in casing and supported by a tubing hanger at its upper end. The tubing hanger lands in a wellhead member, which may be a wellhead housing, a tubing spool mounted on top of a wellhead housing, or a production tree. For various workover and completion operations, the operator needs to be able to pump fluids down the tubing and back up the tubing annulus surrounding the tubing, or vice-versa.
A tubing hanger has a production passage extending through it for communicating with the interior of the production tubing. One type of tubing hanger has a tubing annulus passage extending through the body of the tubing hanger alongside and parallel to the production tubing. In an offshore well completion, the operator may install a plug in the tubing annulus passage before the production tree is installed. After the tree is installed, the operator retrieves the plug with a wireline retrieval tool.
Alternately, a tubing annulus valve could be installed in the tubing hanger before running the tubing hanger. A valve eliminates the need for a riser having passage through which a wire line tubing annulus plug could be run. The valve may be a spring-biased check valve or a hydraulically actuated valve. A number of designs for tubing annulus valves are shown in the patented art. For various reasons, particularly concerns about the reliability, tubing annulus valves are not in widespread use.